There's the pretty widely used hash tag.
And then there's the slightly lesser user hashing.
In my opinion those two are exactly the same, but I don't have the score to suggest a synonym.
One question is where to take the Tag Wiki from. They both have reasonably complete tag wikis that are similar but not identical (personally I find the one from hashing a little bit more informative, but that's probably because I'm a sucker for hyperlinks).